考虑沸腾换热的内燃机流固耦合传热分析

摘要

Oil carbonization was found at the upper side of cylinder liner during development for some engines. To clarify the cause, the head-block coupling heat transfer model of engine is established. Temperature and the convective heat transfer coefficient at coolant side and in-cylinder gas side are obtained by means of CFD simulation and are projected on the structural element surfaces to establish heat transfer boundary condition for the whole engine. Boiling subroutine is written based on BDL boiling heat transfer model to consider the effect of coolant boiling phenomenon on temperature distribution of the whole en- gine. Temperature field of the engine under test condition is analyzed and optimized. It is found that the calculated temperature at the position of oil carbonization is obviously higher than the temperature limit of oil carbonization, and boiling effect at key high temperature region is 15℃ higher. To validate the simulation result, the temperature between upper cylinder liner of baseline and optimized case was measured on test bench. Results show that the simulation result considering boiling effect is close to the experimental data. Oil carbonization phenomenon is eliminated in the optimized case.%某发动机在开发过程中缸套顶部出现机油结焦现象．为分析原因，建立了该发动机缸盖缸体整机耦合传热模型，通过CFD三维仿真获得冷却水侧及缸内燃气侧的温度和对流换热系数分布，并映射至对应结构分析边界单元，建立了整机结构传热分析的边界条件；同时基于BDL单相流沸腾换热模型编写相关子程序考虑了沸腾换热的影响，求解分析了该发动机试验状态下的温度场，并进行了优化．计算表明，结焦现象发生区域温度明显高于机油碳化温度，同时沸腾换热对局部关键高热区影响可达15℃以上．为验证分析结果，分别测量了原方案和优化方案缸套顶部缸间温度，结果表明，考虑沸腾换热后缸间温度计算值与实测数据非常接近，采用优化方案后缸套顶部机油结焦问题得到排除．